Dusting method of screening a cathode-ray tube



United States Patent Office Patented Dec. 1, 1970 3,544,350 DUSTING METHOD OF SCREENING A CATHODE-RAY TUBE Val R. Veirs, Chicago, Ill., assignor to Zenith Radio Corporation, Chicago, Ill., a corporation of Delaware No Drawing. Filed Nov. 2, 1967, Ser. No. 680,021

Int. Cl. H01j 31/20 US. Cl. 11717.5 5 Claims ABSTRACT OF THE DISCLOSURE A phosphor material and a light sensitive, water soluble material, both in finely powdered form, are dusted onto the faceplate of a cathode-ray tube. The dusting takes place through a water mist or spray; alternatively, the .mist is applied after the dusting has taken place. Selected portions of the dusted area are exposed to light and the exposed areas are developed by washing the faceplate with water.

BACKGROUND OF INVENTION The method of the invention is addressed most particularly to screening a color cathode-ray tube by the socalled dusting technique with characteristically distinguishes itself from other forms of screen printing in that the phosphor material is dusted over the image area.

Certainly, screening color cathode-ray tubes by dusting is a known procedure which in its most popular form is practiced by first spraying a liquid layer of a light sensitive material, such as polyvinyl alcohol, over the image area or internal surface of the faceplate of the picture tube. Usually, the polyvinyl alcohol will have been sensitized with ammonium dichromate and a powdered phosphor material is dusted over the light sensitive layer. Alternatively, the light sensitive material may contain some phosphor material in suspension. In any event, the light sensitive area is dried and then exposed and developed. Additional phosphor particles may be dusted onto the exposed and developed elemental areas of the screen.

This process has been in commercial use although it presents troublesome problems of uniformity and may also be critical in respect of the drying of the polyvinyl alcohol. The present invention, while also a dusting process, lends itself to a higher degree of uniformity and simplicity in the manufacture of color cathode-ray tubes.

Accordingly, it is an object of the invention to provide a novel process for screening cathode-ray tubes by means of dusting.

It is a particular object of the invention to improve the dustnig process of screening color cathode-ray tubes.

SUMMARY OF THE INVENTION The screening method of the invention comprises dusting an image area, such as the internal surface of the faceplate of a color cathode-ray tube, with a dry powdered form of a phosphor material and a dry powdered form of a material, such as sensitized polyvinyl alcohol, which is both radiant-energy sensitive and soluble in a particular solvent. The powdered materials are moistened with the solvent during and/ or subsequent to their application by dusting to cause their mixture to adhere to the image area. Thereafter, selected portions of the image area are exposed with radiant-energy to which the sensitive material responds and the area is then rinsed with a solvent to develop the dusted coating at selected portions of the image area.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The organization and sequence of performance of the steps of the inventive method, together with further objects and advantages thereof, may best be understood by reference to the following detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The screening process of this invention may be employed in applying the red, blue and green phosphor elements of a color picture tube; in other words, the character of the phosphor employed is of no consequence and, therefore, will not be referred to in any detail hereafter.

The invention may be practiced by first preparing a powder having as ingredients the phosphor material to be applied to the tube, and also a material which is both radiant-energy sensitive and soluble in a particular solvent. For example, one may mix a quantity of phosphor which radiates green light in response to electron excitation together with a quantity of polyvinyl alcohol and ammonium dichromate. The latter two ingredients are finely ground whereas the phosphor has particle sizes in the range of 2 to 20 microns normally employed in screening picture tubes. The mixture of phosphor and photosensitive resist is a dry powder and is dusted over the entire image area, that is to say, dusted over the entire inner surface of the faceplate of the picture tube since it is now conventional to apply the screen directly to the faceplate. After the image area has received a uniform layer of this mixture by dusting, it is subjected to a spray or mist of the solvent for the radiant-energy sensitive material; for the case at hand the solvent is water and a mist or fine spray of water is applied over the dusted layer. Alternatively, the dusting of the powdered mixture may take place in the presence of a water mist so that the powder and mist fall together on the image area. In either case, there results a moistened layer of phosphor and photosensitive material on the image area which is permitted to dry.

The faceplate thus prepared is now processed in conventional manner to the end that selected portions thereof, and only these selected portions, retain a coating of the green phosphor. Generally, this is accomplished by exposing selected portions of the image area with radiant energy in the familiar lighthouse or exposure table. The exposure takes place through the parallax barrier or shadow mask of the tube which determines the portions thereof which are, in fact, exposed. Thereafter, the Whole image area is washed with the solvent, in this case water, to develop the coating on the selected portions of the image area that have been exposed. These portions as a consequnce of the exposure become insoluble so that the washing removes all of the unexposed coating leaving only the desired selected portions of the image area coated with the phosphor.

For screening one color on a 25" rectangular picture tube in accordance with the invention, one may use a mixture of grams of phosphor in the 5 to 15 microns particle size range, 10 grams of polyvinyl alcohol such as Elvanol grade 5222 and 2 grams of ammonium dichromate.

It is, of course, Well known that phosphor particles may readily be coated and this is done for variety of reasons. It is known, for example, to coat phosphor materials with pigment or filters to control the emission spectrum and it is also known to provide phosphor materials with a coating of silica in order to improve their fiowability or case of application. Any of the known coating techniques may also be advantageously employed in practicing the present invention by first preparing a mixture of finely powdered polyvinyl alcohol and ammonium dichromate in controlled amounts or ratio. The resulting composition may advantageously be coated over phosphor particles and the coated phosphor particles may then be dusted onto the faceplate of the picture tube either in the presence of a water mist or may be moistened after having been dusted on the screen area.

The method of the invention improve the uniformity of the dust-coated layer applied to the screen area of a color tube faceplate preparatory to exposure. It provides simplification of processing over prior techniques in which the sensitive material is first applied to the screen area in liquid form.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim: 1. The method of screening an image area of a cathoderay tube which comprises:

dusting said area with a dry powdered form of a phosphor material and a dry powdered form of sensitized polyvinyl alcohol which is both radiantenergy sensitive and soluble in a particular solvent; moistening said powder material subsequent to the dusting of said screen area with said solvent to cause said materials to adhere to said image area; thereafter exposing selected portions of said image area with radiant energy to which said sensitized polyvinyl alcohol responds; and rinsing said image area with said solvent to develop the dusted coatings on said selected portions of said image area.

2. The method of screening a cathode-ray tube in accordance with claim 1 in which said phosphor material and said sensitized polyvinyl alcohol are intimately mixed and their admixture is dusted on said image area.

3. The method of screening a cathode-ray tube in accordance with claim 1 in which a mist of said solvent is applied to said image area after said powdered materials have been dusted thereon.

4. The method of screening a cathode-ray tube in accordance with claim 1 in which said phosphor material is first coated with said sensitized polyvinyl alcohol and then dusted onto said image area.

5. The method of screening a cathode-ray tube in accordance with claim 1 in which said sensitized polyvinyl alcohol is a finely ground admixture of polyvinyl alcohol and ammonium dichromate and in which said solvent is Water.

References Cited UNITED STATES PATENTS 2,837,429 6/1958 Whiting 117-335 XR ALFRED L. LEAVITT, Primary Examiner WAYNE F. CYRON, Assistant Examiner US. Cl. X.R. 

